So I graphed out the Short term, Long Term, and O2 readings both Pre and Post adding the Volvo MAF.
Prior to adding the MAF I had worked through a list of items trying to clean up some pinging and slightly rough 1000 rpm range, as well as a constantly negative Long term fuel trim and a more often than not negative short term fuel trim.
I'll be the first to say I really don't know much about the fuel trims. As always I'm open to any advice or learnings other have to offer.
I replaced the O2 sensor and ran a tank with 2 bottles of Seafoam at about the same time so cant separate those impacts. After doing so the pinging was dropped from 1500 down to around 1000 and also largely reduced in magnitude. The roughness at 1000 was reduced by half. O2 readings became more responsive and short term fuel trims looked to become more balanced. Long term fuel trims remained negative at all times.
After installing the Volvo MAF the Pinging and 1000 roughness seem maybe slightly improved, but just might be wishful thinking. Short term fuel trims have seemed to shift slightly toward the negative on average and long term fuel trims have made a large shift positive and now aren't always negative. The response throughout the throttle range seems smoother to me.
I've only got 1/4 tank into the Volvo MAF so its a bit early to judge.
At no time during any of this have I ever had an engine light or error code. Its just my own seat of the pants assessment that I didn't like how the engine was running.
Pic came out small. Blue is Short, orange is Long, and grey is O2.
NOTE:
Just so I'm not leaving loose ends. Further testing shows LTFT is still rather negative at lower RPMs and then improves as RPM's increase. I am running the later brown injectors in a 98 that originally had grey injectors. My plan is to send the grey injectors off for servicing and then install them and see.